It is known that non-linear interactions and, at higher pulse energies or energy densities, a photodisruption in particularly optical materials or tissue can be generated with the help of femtosecond laser radiation.
In everyday clinical life, for example, this is utilized in eye-surgical lasers such as the “Visumax” from Carl Zeiss Meditec AG. Here the laser system is provided with a femtosecond (fs) laser beam source, the pulse energy of which is adjusted beforehand at a predetermined repetition rate (e.g., 500 kHz) of the laser pulses in a relevant range of, e.g., 50 nJ-5 μJ in order to always reliably generate a photodisruption in the tissue. With regard to a treatment of the cornea of the eye, a minimal focal diameter in the 1 μm an range can be achieved with a comparatively large numerical aperture of the focusing optics (approximately 0.3).
Optimal parameters have become known for the fs laser therapy of the crystalline lens which ensure quick treatment and minor collateral damages (EP 1212022 B1). With apertures of approximately 0.2, focal diameters of approximately 5 μm can be achieved. Such an arrangement is also known from EP 1663087 or from the applicant's WO 2008/017428, the entire content of which is hereby incorporated by reference.
For the treatment of the eye fundus or the retina, only coagulation lasers (e.g., frequency-doubled Nd:YAG with a wavelength of 532 nm or also 561 and 659 nm) are known which can coagulate eye tissue, particularly of the retina, and also atrophy bleedings through thermal effects.
With an approximate volume of 80%, the vitreous humor is the largest structure of the eye. It consists of a gelatinous complex of hyaluronic acid, water, and a collagen framework. In the course of life, the vitreous humor undergoes an aging process which causes significant structural changes. Those changes are essentially a type of liquefaction of the vitreous humor which can result in detachments of the vitreous humor from the surrounding layers of the eye, particularly the retina and the capsular bag of the lens, which can entail medical complications.
A frequent serious complication is a retinal detachment which can occur in the periphery of an incomplete vitreous detachment. It is frequently induced by tensile forces of vitreous humor strands which connect the partially detached vitreous humor to the retina.
Such complications are commonly treated with a vitrectomy, wherein the eye is opened up and the vitreous humor surgically removed. However, this surgical procedure causes great stress for the patient, entails high costs due to the necessary hospital treatment and risks during the procedure.
It has been demonstrated in rare cases that traction causing vitreous humor strands can be severed with focused radiation from an Nd:YAG laser, thereby avoiding a vitrectomy [D. Schmidt, “Macular-threatening fraction detachment of the retina in a diabetic proliferative retinopathy, treated by laser,” International Ophthalmology, 21, 99-106, 1997]. The severing is effected by the pressure wave of photodisruptions which are caused by the high pulse energies in the mJ range at pulse durations of a few ns. Said pressure waves also damage the surrounding tissue, making the use of this method impossible in immediate proximity of the retina. The laser spot is still placed manually by the physician after observation through a slit lamp microscope.